Power converters are commonly used in a machine for motor control. Power converters use current sensors in series with the motor windings to provide feedback information characteristics of the motor. The current sensor performance parameters, such as scaling, frequency response, linearity and polarity are critical to the performance of the power converter when switching between high energy levels. If there is a malfunction in the sensor or wire harness, the power converter may become uncontrollable, and the motor system driven by the power converter may be shut down. Additionally, permanent damage may also be caused to the power components. Thus, it may be desirable to test the current sensors and their wire harness before applying high-voltage to the power converter.
Furthermore, it may also be important that the testing system is accurate. In particular, in the event of sensor or wire harness faults, it may be helpful to accurately locate the position of the fault, based on the measurements obtained by the current sensors. To accurately determine whether a particular current sensor fails, a normal range of the current value needs to be decided by properly accounting for each load characteristic. In addition, reliability is another factor to consider in the design of the testing system. In particular, it may be desirable to use low-voltage and current-limiting power supply to drive the test, so that test could be performed without damaging components, in the event of wire harness fault or current sensor failure. Finally, convenience of use is yet another desirable characteristic for the testing system. For example, the test may be performed automatically without any re-wiring of the circuit or connection of external components or without requiring special skills.
A system for testing current sensors in an electric machine is described in U.S. Pat. No. 6,989,641 to Schulz et al. (“the '641 patent”). The '641 patent describes a system for controlling a three-phase electric machine having current sensors for less than each of its phases. The control system includes a three-phase electric machine, an inverter to provide current to the electric machine, and a processor to control the inverter to test the current sensors associated with the electric machine.
The current sensor testing method described in the '641 patent includes operating the inverter to apply a testing voltage waveform to the windings with current sensors, sampling current waveforms from the current sensors, and performing tests on the waveforms to determine whether a fault exists. In one instance, the magnitudes of the current waveforms, sampled from two current sensors in the testing windings, are compared. A threshold is used to determine whether the difference between the two current magnitudes is within tolerance. If the difference is higher than the threshold, a fault may exist in the tested windings. In another instance, a test waveform is synthesized and applied to two phases in a three-phase electric machine. All measured waveforms from the two current sensors are summed together, and compared to another threshold waveform to determine whether a fault exists.
Although the control system described in the '641 patent may be effective for testing current sensors associated with an electric machine, it may be problematic. For example, the current sensor test described in the '641 patent may not be capable to provide early indication of a fault before high-voltage is applied. As a result, power electronic devices as well as the motor may be damaged due to current sensor failure and/or wiring faults. Furthermore, although the system described in the '641 patent may be able to indicate whether a fault exists, it may be incapable to accurately determine which sensor, or sensors, fail. In addition, the system described in the '641 patent may provide insufficient reliability. For example, the system described in the '641 patent uses a DC source directly coupled to the inverter without any current limiting components. As a result, components in the tested windings, for example, power electronic devices, may be damaged in the event of wire harness fault or current sensor failure. Finally, the system provided by the '641 patent may not be convenient to use.
The disclosed power converter current sensor testing system is directed towards overcoming one or more of the shortcomings set forth above.